Apes and humans differ
from all of the other primates in that they lack external tails.
They also are more intelligent and more dependent for survival on learned
behavior patterns. There are several internal body
differences as well, such as the absence of an appendix in monkeys. In
addition, the lower molar teeth of apes and humans have five cusps, or
raised points, on their grinding surfaces. This is known as a Y-5
pattern because the area between the cusps roughly is in the shape of the
letter Y. Monkeys only have four cusps on their lower molars.
The shoulder anatomy of apes and humans also differs from other primates.
This difference and the advantages it provides for traveling through the
trees are described below.

The
apes and humans are members of the same superfamily, the Hominoidea.
Subsequently, they are referred to as hominoids.
Until the last few years, humans were separated into
their own family within this superfamily because
it was believed that we are significantly different from the apes.
However, recent genetic studies and
discoveries from the fossil record have made it clear that some of the apes
are more similar to humans than previously believed. Subsequently, the
living hominoids are now commonly classified into only two families with
humans grouped with the great
apes in the second family:

The smallest and the most
arboreal apes are the 12-13 species of gibbons.Because
of their diminutive size, these members of the family
Hylobatidae
are also referred to as the "lesser apes."Most adult gibbons
are only about 3 feet (90 cm.) tall standing upright and 12-20
pounds (5.5-9 kg.) in weight.
Males in the biggest gibbon species, known as siamangs,
are up to 30 pounds (13.5 kg.).
Siamangs are different enough from other gibbons to be in their own genus.All gibbons are very slender. Long bushy
hair on their bodies makes them look stockier than they actually are.
Gibbons have little sexual
dimorphism in body size, with the exception of siamangs.
However, the sexual dimorphism of siamangs is slight compared to that of the
great apes.

Siamang
brachiating

Gibbons are excellent brachiators. That is, they move
around in trees by swinging under branches with a hand over hand motion.
This is also referred to as suspensory climbing. At times,
gibbons walk bipedally, or two footed, on top of branches. However, they are more
efficient at brachiation, and 90% of their locomotion is by this means.
Gibbons have long arms with sturdy rotary cup shoulder
joints, comparatively short legs, permanently curved fingers, and light weight bodies.
The rotary cup joints allow them to easily raise their arms straight up
above their heads. They also allow
gibbons to swing long distances from branch to branch with little effort. Each
swing can transport a gibbon 20 feet (6 m.)at speeds approaching 35 miles (56 km.) an hour.
Their upper torsos are flattened from front to back and their shoulders are
far apart, giving them a mechanical advantage in thrusting each arm forward
in turn.

Brachiation is a
rare ability for primates. None of the prosimians do it.
Among the monkeys, only a few New World species have the capability, and
they don't use it as frequently as the gibbons. All of the great
apes have the anatomical characteristics that allow brachiation, but
most of them rarely use this mode of locomotion because they are too
heavy to be supported by small branches. Humans also have retained
most of the upper body traits that allow us to brachiate, though our
legs grew significantly longer and more muscular as we became habitually
bipedal. As a consequence of weakened arm muscles and added weight
from our legs, we now are inefficient brachiators at best.
However, our small children are still light enough to enjoy swinging on
playground "monkey bars".

One other
anatomical feature sets the gibbons apart from the other apes.
They have ischial callosities
like many of the Old World monkeys. No great ape has them.

Gibbons are monogamous
in their mating
patterns and form nuclear family groups. That is to say, their communities
consist of a single mated pair of adults with their juvenile offspring. They live in
well defined territories in the tree tops and rarely go down to the forest floor.
Adults regularly defend their territory against others of their species with
piercingly loud whooping and hooting vocalizations, much like the indris of Madagascar and
the howler monkeys of the New World. However, the calls
of the latter two primates sound very different. The calls of
different gibbon species are easily distinguished from each other as well. When
they are vocalizing, the front of the necks of gibbons and siamangs expand
with air, much like the flexible bag on a bagpipe.

Orangutansare the largest and the rarest of the Asian apes.Males
often grow to
175-200 pounds (80-90 kg.) and 4½ feet
(1.4 m.) tall. At this size, they are usually too large to cross from
one tree to another by the branches and must go down to the ground and walk
quadrupedally between them.There is marked sexual dimorphism among the orangutans.
Males have huge fleshy pads framing the upper part of their faces.In addition, females weigh
only about half as much as the males
(73-99 lbs or 33-45 kg.). Being lighter, females and juveniles often stay in
the trees and use a leaning form of brachiation--they carefully shift their body weight to
bend a supporting branch and then grab the next one before the first one breaks.

Orangutans have largely hairless
faces, but the rest of their bodies are covered with long reddish brown
hair. The body hair of adult males becomes so long and intertwined
that it appears almost to be in unkempt "dreadlocks".

Orangutans
are intelligent and generally peaceful vegetarians. Most
of the time, they live solitary lives quietly browsing fruits and leaves
high up in trees.
They are nearly as intelligent as the African apes, but have much more
introverted personalities.

Unfortunately,
the orangutans are in danger of extinction in the wild because they are hunted for the
illegal international pet trade. Their forest territories are also being rapidly cut
down for the lumber and cleared by burning for farming, especially in Indonesia where
most of them live.Conservation International
estimates that the 15,000
remaining Indonesian orangutans are currently disappearing at a rate of 1,000 per
year. When population size shrinks, there is a
corresponding decrease in genetic diversity. Species that have little
genetic diversity are more easily driven to extinction by a changing
environment. The loss of habitat has decimated gibbons in Indonesia as well. However, they are not at as much a risk
of becoming extinct because their range extends widely over Southeast Asia.

The largest apes are the
gorillas of Africa. Adult males are
5½- 6 feet
(1.7-1.8 m.)
tall and have 9-10 foot (2.7-3.0 m.) arm spans. They have massive heads with heavy, thick muscles
on top that are used to close crushing jaws. Their bodies are stout and very
muscular.

Knuckle walking(subadult male lowland gorilla)

Like humans, gorillas are
terrestrial animals. They are
quadrupedalknuckle walkers. That is, they walk
on the soles of their feet but not on the palms of their hands.They bend their fingers and support the
upper end of their
bodies with their knuckles instead of their open palms.

They are
shy, peaceful vegetarians who usually flee from humans and
rarely fight even among themselves. They live in family groups consisting of a dominant adult male
with several adult female mates and their children.
These groups grow over time to 20 or more individuals. Subadult males are tolerated in the
family as long as they are not actively competing with the dominant male for
mates. Gorillas are highly sexually dimorphic.
Adult males average about 350 pounds (160 kg.) and reach 400
pounds (181 kg.) in the wild,
while most adult females are only
about 155 pounds (70 kg.) and much less muscular.

There are
three varieties, or subspecies, of gorillas. The rare mountain gorilla
variety lives at high
altitude in sparse woodlands in the mountains of Central Africa.
As of 2011, there were only 786 of them still alive. The more
numerous lowland gorilla varieties live in the dense forests ofWest Africa.Most zoo
gorillas are of the lowland varieties.

Femalelowland gorilla

Common chimpanzee

Mutualgrooming
(common chimpanzees)

The
common chimpanzees
more closely resemble humans than do the gorillas. Male chimps grow to 5½ feet
(1.7 m.) tall
and average about 100 pounds (45 kg.) with 6 foot
(1.8 m.) arm spans, while females are
usually only around 82 lbs. (37 kg.) and are less muscular.
Chimpanzees are comfortable
walking quadrupedally on the ground in addition to
climbing in trees. They are
knuckle walkers like
gorillas. The natural habitat of chimpanzees includes both tropical forests and
bordering savannas
in Africa.

Chimps are
intelligent animals with generally pleasant personalities. However, the males are
less peaceful than the smaller females. This behavior difference is typical of most
primate species, including humans. The chimpanzee diet is usually at least 90% vegetarian. Males
are more likely to eat meat than are females, although chimp hunting skills are
relatively poor.

Chimpanzees
live in fluid societies of 10-50 individuals without
monogamous mating bonds. Membership changes through time as
females move from one community to another apparently
seeking new mates. In contrast, males usually stay together
in their natal community throughout their lives and act as a group in
defending the food resources of their territory
against incursions by other chimpanzee communities.
These interactions can be quite noisy, violent, and sometimes fatal.

Bonobos
are close relatives of common chimpanzees in the same genus, Pan.
Their similarity is due to the fact that they had a common ancestor only
about two million years ago.
Bonobos are sometimes referred to as pygmy
chimpanzees. Despite this name, they are only slightly smaller than the common
chimps. Bonobos usually have blacker hair with tufts at the side of their faces, longer
arms and legs, as well as slimmer bodies.
Their high pitched vocalizations are also quite different from those of the common
chimpanzees. Like many of the Old World monkey species, adult female bonobos
normally have prominent "sexual skins." However, unlike monkeys, bonobo
females are sexually receptive throughout the year.

Female
bonobo

Bonobofemale sexual skin

Bonobos have fluid social groupings
similar to the common chimpanzees, although bonobos are less excitable and aggressive.
Male-female alliances also are more important for bonobos. Older females at times
even become group leaders. Bonobos are unique among
nonhuman primates in primarily engaging in sexual intercourse face to face.
Gorillas do it occasionally. Both heterosexual and homosexual intercourse are common
among bonobos. Copulation occurs
frequently as a means of reducing tension in the community
and has become recreational for them. In this and
other traits, bonobos are quite similar to humans.

Today, the bonobo
range is limited to the forests south of the Zaire River in West Central
Africa, and there are considerably fewer of them than the
common chimpanzees.

Chimps and Bonobos--an explanation of how
they became different speciesThis link takes you to a
video at an external website. To return here, you must clickthe"back" buttonon your browser
program.
(length = 3 mins, 47 secs)

Primates At Risk

Common
chimpanzees are the most successful of all apes in that there are more
of them and they have the widest geographic range. However, their
numbers have been significantly reduced. A century ago, there were
millions of them in the wild. Today, there are less than 200,000.This sharp decline apparently has been mostly due to the rapid increase in
human populations and the accompanying natural habitat decimation. An
additional factor has been the desire of many people in
West and Central Africa
to eat
chimpanzees and other non-human primate species. At least 4,000
chimpanzees are killed for their meat every year.
Most apes and monkeys are relatively large, noisy animals that are easy
targets for hunters.Chimpanzees and gorillas have suffered devastating Ebola epidemics as
well. During 2002 and 2003, approximately 5,000 gorillas succumbed to
this highly contagious, almost always fatal disease. The lowland
gorilla population has dropped by at least 80% over the last 3 generations.
Only 100,000-125,000 survive today. The bonobos are at an even greater risk of disappearing since there may be only
about 6,000 of them remaining in the wild.
The African apes
have the misfortune of living mostly in nations in which wildlife protection has been
severely disrupted by civil wars and the breakdown of
effective national authority over the last two decades.
It is unlikely that the populations of these apes would be able to spring back rapidly
even if they were more carefully protected because they have low
reproductive rates. Under the best conditions, adult female chimps
usually only have one baby every 5 years. The other great apes are
similar.

The great apes are not alone in being
threatened by humans. The International Primatological
Congress has estimated that 48% of primate species are in danger of extinction
within the next decade. Many will disappear with little known about
them. They are at their greatest risk in Asia. The percentage of
threatened primate species is 79% in China, 83% in Laos, 84% in Indonesia,
86% in Vietnam, and 90% in Cambodia. In most parts of the world, the
main threat is loss of habitat due to forest clearance. However,
conservation efforts have had some successes in Brazil. The numbers of
Golden lion tamarins and black lion tamarins there have been increasing to
the point that these species are no longer considered critically endangered.
Also on the hopeful side is the recent discovery of approximately 125,000
western lowland gorillas in a largely unexplored forest region of northern
Democratic Republic of Congo. Impacts on this area by humans have been
minimal so far.